A multilayer ceramic capacitor as an example of electronic devices is composed of an element body having a multilayer structure, wherein a plurality of dielectric layers and internal electrode layers are alternately arranged, and a pair of external terminal electrodes formed on both end portions of the element body.
To produce the multilayer ceramic capacitor, first, a pre-firing element body is produced by alternately stacking a plurality of pre-firing dielectric layers and pre-firing internal electrode layers by exactly necessary numbers, then, after firing this, a pair of external terminal electrodes are formed at both end portions of the fired element body.
A ceramic green sheet is used as the pre-firing dielectric layer, and an internal electrode paste in a predetermined pattern and a metal thin film, etc. are used as the pre-firing internal electrode layer.
The ceramic green sheet can be produced by the sheet method and orientation method, etc. The sheet method is a method of producing by applying a dielectric coating material including dielectric powder, a binder, plasticizer and organic solvent, etc. on a carrier sheet, such as PET, by using the doctor blade method, etc., heating and drying. The orientation method is a method of producing by performing biaxial orientation on a film shaped molded item obtained by extruding performing extrusion molding on a dielectric suspension wherein dielectric powder and a binder are mixed in a solvent.
The internal electrode paste layer in a predetermined pattern is produced by the printing method. The printing method is a method of applying and forming a conductive material including metal, such as Pd, Ag—Pd and Ni, and a conductive coating material including a binder and an organic solvent, etc. to be a predetermined pattern on a ceramic green sheet. A metal thin film having a predetermined pattern is produced by a thin film method, such as sputtering.
As explained above, when producing a multilayer ceramic capacitor, the pre-firing dielectric layers and the pre-firing internal electrode layers are fired at a time. Therefore, the conductive material included in the pre-firing internal electrode layer is required to have a higher melting point than a sintering temperature of a dielectric powder included in the pre-firing dielectric layer, not to react with the dielectric powder, and not to be dispersed in a fired dielectric layer, etc.
Conventionally, to satisfy the demands, Pt, Pd and other precious metals are used as the conductive material included in the pre-firing internal electrode layer. However, precious metals themselves are expensive, so that there is a disadvantage that a finally obtained multilayer ceramic capacitor becomes costly. Thus, conventionally, the sintering temperature of the dielectric powder was lowered to 900 to 1100° C., and an Ag—Pd alloy, Ni and other inexpensive base metals are used as the conductive material included in the pre-firing internal electrode layer.
In recent years, as a variety of electronic equipments become more compact, electronic devices to be installed inside the electronic equipments have become more compact and larger in capacity. To pursue a more compact multilayer ceramic capacitor having a larger capacity, it is required to stack thin internal electrode layers with less defectives, not to mention the dielectric layers.
However, when taking the case of using Ni as the conductive material included in the pre-firing internal electrode layer as an example, the Ni has a lower melting point than that of the dielectric powder included in the pre-firing dielectric layer. Accordingly, when firing the both at a time, there arises a big difference between their sintering temperatures. When sintering at a high temperature in the case where there is a big difference between sintering temperatures, cracks and delamination of the internal electrode layers arise, while when sintering at a low temperature, a firing defect of the dielectric powder may arise.
Also, when a thickness of the pre-firing internal electrode layer becomes thinner, during firing in a reducing atmosphere, Ni particles included in the conductive material become spherical due to grain growth and gaps arise between adjacent Ni particles, which are connected to each other before firing, and vacancy is generated at any part, as a result, it becomes difficult to form a continuous fired internal electrode layer. When the internal electrode layer after firing is not continuous, there is a problem that a capacitance of a multilayer ceramic capacitor declines.
The Japanese Unexamined Patent Publication No. 3-126206 describes a method of alloying internal electrode layers to prevent breaking of internal electrodes. Note that in the Japanese Unexamined Patent Publication No. 3-126206, it is considered that control of alloying is difficult in the thin film formation method and an internal electrode layer is prepared as a metal multilayer film, and alloying is performed after a firing step.
However, the Japanese Unexamined Patent Publication No. 3-126206 does not disclose what kind of metal is used for alloying when using an internal electrode including nickel as the main component to suppress grain growth of nickel particles in the firing step, so that it is possible to prevent them from becoming spherical and prevent electrodes from breaking. Depending on compositions of respective multilayer metal films, the sintering temperature adversely becomes low and grain growth of the nickel particles cannot be suppressed in the firing step.
Also, when a metal film contacting ceramic is poor in a wettability and adhesiveness in the configuration of each multilayer metal film, spheroidizing and breaking adversely proceed and a capacitance as a capacitor declines.
Also, the Japanese Unexamined Patent Publication No. 10-214520 proposes a conductive paste containing nickel as the main component and metallocene expressed by a general formula M[(C5H5)2] (M is at least one kind of Ru, Os, Pd, Cr and Co).
However, in the Japanese Unexamined Patent Publication No. 10-214520, since the conductive paste contains an organic metal compound, there is a problem that organic components are decomposed by a catalytic action and cracks arise on an element body, etc. Particularly, when an adding quantity of the organic metal compound exceeds 0.1 mol % as a metal amount, particularly, the incidence of cracks tends to become high.